(Invited) Nanoscale Surface Coatings for High-Performance Nickel-Rich LiNixMnyCozO2 Cathodes Via Atomic Layer Deposition

Abstract

Nickel (Ni)-rich LiNixMnyCozO2 (NMCs, x + y + z = 1, x ≥ 0.6) are among the most promising cathodes for next-generation lithium-ion batteries (LIBs) and beyond, ascribed to their high capacity and low cost. With increasing Ni contents, however, NMCs become more challenging for commercialization, due to a series of aggravated issues. In addressing these issues, surface coating has been remaining as a facile and effective strategy. In this regard, atomic layer deposition (ALD) has been recognized as a unique surface-coating technique in the past decade, featuring its unrivaled capability for uniform and conformal coatings.1-3 ALD also is to date the only technique that can perform on either prefabricated electrodes or electrode powders directly. In searching for new solutions to the issues of NMCs, recently we have conducted a series of studies on different coatings, including oxides and sulfides via ALD.4-8 Our studies revealed that Li-containing oxides are better than Li-free oxides, due to improved ionic conductivity. They both served multiple roles for protecting NMCs, including as a physical barrier to mitigate undesirable interfacial reactions, a structural stabilizer to inhibit unfavorable phase transformation, and a robust network to improve mechanical integrity. Very interestingly, we for the first time have discovered that, compared to oxide coatings, sulfides are more advantageous. Our studies have revealed that, while acting similar roles as oxides, sulfides have some unusual protection effects for better performance of NMCs. We found that sulfides could experience some favorable phase transition during charge-discharge processes, which transferred sulfides into sulfites or/and sulfates. This transition process could particularly remove the released oxygen from NMCs and thereby protected electrolytes from oxidation. We further demonstrated that this transition is significant for achieving long-term stable cyclability of NMCs. Thus, our studies have greatly widened the search of surface coatings and provided new solutions for next-generation LIBs and beyond.